Combined open loop/closed loop method for controlling uplink power of a mobile station

ABSTRACT

A method and apparatus are disclosed comprising a combined open loop/closed loop uplink power control scheme for E-UTRA. The combined open and closed loop method for UL intra-cell PC controls the wireless transmit receive unit (WTRU) transmit power spectral density (PSD), PSD Tx , (e.g. power per RB).

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional Application Ser.No. 60/893,575, filed on Mar. 7, 2007, U.S. provisional Application Ser.No. 60/895,561, filed Mar. 19, 2007 and U.S. provisional ApplicationSer. No. 60/945,286, filed Jun. 20, 2007, which are incorporated byreference as if fully set forth.

FIELD OF INVENTION

The present invention is related to wireless communication systems.

BACKGROUND

For the evolved universal terrestrial radio access (E-UTRA) uplink (UL),there are several transmit power control (TPC) proposals that weresubmitted to third generation partnership project (3GPP) long termevolution (LTE) Work Group 1 (WG1). These proposals can be generallydivided into (slow) open loop TPC and slow closed loop or channelquality information (CQI)-based TPC.

Open loop TPC is based on pathloss measurement and system parameterswhere the pathloss measurement is performed at a wirelesstransmit/receive unit (WTRU) and the system parameters are provided byan evolved Node-B (eNodeB).

Closed loop TPC is typically based on TPC feedback information, (such asa TPC command), that is periodically sent from the eNodeB where thefeedback information is generally derived using signal-to-interferencenoise ratio (SINR) measured at the eNodeB.

Open loop TPC can compensate for long-term channel variations, (e.g.pathloss and shadowing), in an effective way, for instance, without thehistory of the transmit power. However, open loop TPC typically resultsin pathloss measurement errors and transmit power setting errors. On theother hand, slow closed loop or CQI-based TPC is less sensitive toerrors in measurement and transmit power setting, because it is based onfeedback signaled from the eNodeB. However, slow closed loop orCQI-based TPC degrades performance when there is no available feedbackdue to UL transmission pause, or pauses in the feedback transmission orchannel variations are severely dynamic.

For the UL E-UTRA, there are several intra-cell PC proposals, which havebeen submitted to third generation partnership project (3GPP) long termevolution (LTE) work group (WG)#1. These proposals can be generallydivided into slow open loop PC and slow closed loop, (or CQI based PC).Open loop PC can compensate for long-term channel variations, (e.g.,pathloss and shadowing), in an effective way, for instance, without thehistory of the transmit power, but it typically suffers from errors inpathloss measurement and transmit power setting. On the other hand, slowclosed loop or CQI based PC is less sensitive to errors in measurementand transmit power setting, because it is based on feedback signaledfrom the eNodeB. However, it degrades performance when there is noavailable feedback due to UL transmission pause or pauses in thefeedback transmission.

As such there exists a need for an improved method of transmission powercontrol.

SUMMARY

A method and apparatus are disclosed comprising a combined openloop/closed loop uplink power control scheme for E-UTRA. The combinedopen and closed loop method for UL intra-cell PC controls the wirelesstransmit receive unit (WTRU) transmit power spectral density (PSD),PSD_(Tx), (e.g. power per RB).

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding of the invention may be had from thefollowing description of a preferred embodiment, given by way of exampleand to be understood in conjunction with the accompanying drawingswherein:

FIG. 1 is an example wireless communication system;

FIG. 2 is an example block diagram of a transmitter and receiverconfigured to implement the disclosed power control (PC) method;

FIG. 3 shows an example of the timing of the disclosed combined PCmethod;

FIG. 4 shows an example of the disclosed combined power control methodwhen inter-TTI is one (1);

FIG. 5 shows another example of the disclosed combined PC timing wheninter-TTI is two (2);

FIG. 6 shows an example of the disclosed combined PC scheme, includingdiscontinuous transmission (DTX);

FIG. 7 shows an example of the disclosed PC method for the nth updateinstant; and

FIG. 8 shows a flow diagram of the disclosed combined open-loop andclosed method of determining the TPC.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “wireless transmit/receiveunit (WTRU)” includes but is not limited to a user equipment (UE), amobile station, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of user device capable of operating in a wireless environment. Whenreferred to hereafter, the terminology “base station” includes but isnot limited to a Node-B, a site controller, an access point (AP), or anyother type of interfacing device capable of operating in a wirelessenvironment.

FIG. 1 shows an example wireless communication network (NW) 10comprising a WTRU 20, one or more Node Bs 30, and one or more cells 40.Each cell 40 comprises one or more Node Bs (NB or eNB) 30 including atransceiver 120 configured to implement a disclosed method of transmitpower control (TPC). WTRU 20 comprises a transceiver 110 also configuredto implement the disclosed TPC method.

FIG. 2 is a functional block diagram of transceivers 110, 120 configuredto perform the disclosed method. In addition to components included in atypical transmitter/receiver, i.e., a WTRU or Node-B, transceivers 110,120 include processors 115, 125, receivers 116, 126 in communicationwith processors 115, 125, transmitters 117, 127 in communication withprocessors 115, 125 and antenna 118, 128 in communication with receivers116, 126 and transmitters 117, 127 to facilitate the transmission andreception of wireless data. Additionally, the receiver 126, transmitter127 and antenna 128 may be a single receiver, transmitter and antenna,or may include a plurality of individual receivers, transmitters andantennas, respectively. Transmitter 110 may be located at a WTRU ormultiple transmitting circuits 110 may be located at a base station.Receiver 120 may be located at either the WTRU, Node B, or both.

The disclosed method of TPC comprises a combined open loop and closedloop scheme for uplink (UL) intra-cell power control. The methodcomprises controlling the WTRU transmit power spectral density (PSD) orPSD transmit (PSD_(Tx)), e.g., power per resource block (RB), or theWTRU transmit power using open loop and a-periodic closed loop powercontrol (PC) for both UL data channel control channels and soundreference symbols (SRS). UL channel quality indicator (CQI) (orModulation Coding Set (MCS)/grant information) is used at the WTRU tocorrect open loop and/or measurement errors, assuming the UL MCS/grantrepresents the signal to interference and noise ratio (SINR) received atthe Node-B. If no CQI is available, then only the open loop isconducted. Implicit command signaling, e.g. no signaling overhead, forthe closed loop component can be used. Alternatively, exploit TPCcommand signaling in DL control channel can be used for the closed loopcomponent. Additionally, the disclosed method is capable of correctingopen loop errors quickly, resulting in good performance.

The disclosed method, as indicated above, comprises controlling the WTRUtransmit power spectral density (PSD) or PSD transmit (PSD_(Tx)), e.g.,power per resource block (RB) or transmit power. It should be noted thatalthough the disclosed method includes controlling the transmit PSD, itis equivalent to controlling the transmit power. PSD_(Tx) is defined as:PSD _(Tx) =PSD _(open)+α·Δ_(closed)+Δ_(MCS);  Equation (1)where PSD_(open) represents pathloss based open loop PSD in dBm;Δ_(closed) is a power correction factor which is determined based on theclosed loop component, to be disclosed in detail hereinafter; Δ_(MCS) isa power offset per granted MCS; and α is a weighting factor to enable(α=1) or disable (α=0) the closed loop component, depending on theavailability of the downlink (DL) control channel, which embeds closedloop PC (correction) command signaling (explicitly or implicitly). Theweighting factor may be determined by WTRU 20 via autonomously detectingthe presence of the closed loop PC command signaling. Alternatively,WTRU 20 is informed via higher signaling from eNodeB 30 with regard towhere the command signaling exists. The transmit PSD should not exceedthe maximum transmit PSD, PSD_(max), where PSD_(max) is derived based onthe maximum allowed power, P_(max), that depends on the UE power class,such as PSD_(max)=P_(max)/M where M is the size of the UL channelresource assignment expressed in number of resource blocks valid for agiven subframe.

The proposed intra-cell PC scheme in Equation (1) may use an absolutepower correction factor compared to the open loop based PSD. FromEquation (1), the WTRU Tx PSD at the n^(th) update instance can beexpressed as:

$\begin{matrix}\begin{matrix}{{{PSD}_{Tx}(n)} = {{{PSD}_{open}(n)} + {\alpha \cdot {\Delta_{closed}(n)}} + {\Delta_{MCS}(n)}}} \\{= {{{PSD}_{Tx}^{\prime}\left( {n - 1} \right)} +}} \\{\left( {{{PSD}_{open}(n)} - {{PSD}_{open}\left( {n - 1} \right)}} \right) + {\alpha \cdot}} \\{{\left( {{\Delta_{closed}(n)} - {\Delta_{closed}\left( {n - 1} \right)}} \right) + {\Delta_{MCS}(n)}};}\end{matrix} & {{Equation}\mspace{14mu}(2)}\end{matrix}$where PSD′_(Tx)(n−1) represents the (n−1)^(th) Tx PSD without the poweroffset per granted MCS, which is given byPSD′_(Tx)(n−1)=PSD_(Tx)(n−1)−Δ_(MCS)(n−1).

Typically, the power offsets for the individual granted MCS are known byboth the WTRU and the eNodeB.

Processor 115 of WTRU 20 combines pathloss based open loop and closedloop PC to determine PSD_(Tx). In accordance with the disclosed method,WTRU 20 first performs open loop PC based on path loss measurement andsystem parameters (PSD_(open)). PSD_(open) is calculated as follows:PSD _(open) =PSD _(target) + L (dBm);  Equation (3)where

-   -   PSD_(target) is a target PSD received at serving eNodeB 30,        which is preferably a WTRU (or a sub-group of WTRUs)-specific        parameter. The target PSD may be adjusted through an outer loop        mechanism according to Quality of Service (QoS) (e.g., target        block error rate (BLER)), and also a function of the pathloss        measurement, to compensate for a fraction of the pathloss. The        signaling of the target PSD target is done via higher layer        signaling from Node B 30 to WTRU 20 upon adjustment on a slow        rate basis; and    -   L is the filtered pathloss in dB, including shadowing, from        serving eNodeB 30 to WTRU 20, where WTRU 20 first measures the        instantaneous pathloss based on the DL reference signal (RS)        whose transmit power is known. WTRU 20 then applies a filtering        method to the pathloss. For example, the filtered pathloss at        the k-th instance, L _(k), can be calculated as        L _(k) =ρ· L _(k-1)+(1ρ)·L _(k);  Equation (4)    -   where L _(k-1) and L_(k) represent the filtered pathloss at the        (k-1)-th instance and instantaneous pathloss at the k-th        instance; ρ is a filter coefficient, 0≦ρ≦1, which is generally        determined by WTRU 20, depending on pathloss variation, fast        fading rate, the time of UL transmission, and others, for        example. The filtering for pathloss can be done in PHY layer        and/or L 2/3 layer.

Once WTRU 20 determines the open loop component, processor 115calculates the closed loop component. As those having skill in the artknow, there are open loop related errors, including the pathlossestimation error due to non-perfect reciprocity in UL and DL in FDD andthe WTRU Tx impairment due to non-linear power amplifier. To compensatefor such errors and to maintain the quality of the power controlledchannel along with the target quality, the WTRU applies a correction tothe open loop based PSD in a form of closed loop PC as in Equation (1),(or Equation (2)).

Serving eNodeB 30 determines a WTRU specific (absolute and/oraccumulated) PC correction command for each UL scheduled WTRU (or asub-group of scheduled WTRUs). Preferably, eNodeB 30 uses the powercontrolled data channel as a reference for the correction command. Theresulting correction command is signaled to WTRU 20 (or a sub-group ofthe scheduled WTRUs) through the UL grant, and/or the DL schedulingchannel, sent in the DL Layer 1 or Layer 2 control channels. Thecorrection command may be signaled only in the UL grant associated witha particular (predefined) HARQ process, such as every HARQ process 1.

Upon receiving the correction command(s) at WTRU 20, processor 115 ofWTRU 20 determines the correction factor, Δ_(closed), based on thecorrection command (or accumulated correction commands) set forth as:Δ_(closed) =f(PC correction command(s));  Equation (5)where Δ_(closed) may take on a set of multiple step levels, for example,{+/−4, +/−1 dB} using 3 bits of the command.

Alternatively, eNodeB 30 sends to each scheduled WTRU 20 (or a sub-groupof scheduled WTRUs) a power correction factor using multiple commandbits, such as 3 bits, in the UL grant and possibly in the DL schedulingin the DL control channel, where the correction command is preferablydetermined based on link quality (such as received PSD or SINR) of theUL power controlled data channel (and possibly UL sounding referencesymbol, if available). For example, assuming a set of power correctionfactor values to be {−7, +/−5, +/−3, +/−1, 0 dB} with 3 bits, thecorrection factor may be determined as followΔ_(closed)=└ESINR_(est)−SINR_(target)┘;  Equation (6)where ESINR_(est) and SINR_(target) denotes the effective SINR (ESINR)estimate at the receiver and target SINR, respectively, of the powercontrolled channel(s) in dB. [x] denotes a correction value in thecorrection set, which is nearest to x. The observed samples at theeNodeB for the ESINR estimation include (some of or all) SC-FDMA symbolsof the UL power controlled channel(s), which have been received sincethe last correction command signaling in DL.

To reduce the command signaling overhead, the correction command is notrequired in every UL grant (and every DL scheduling if used). That is,the correction command can be sent on a pre-configured signaling time(e.g., in every N grant channel or every N Transmission Time Interval(TTI) where N is a configurable parameter being less than or equal tothe minimum UL PC update period).

A correction command signaling timing is configured at eNodeB 30 (or ona RRC level) per WTRU basis and is then known at both eNodeB 30 and WTRU20 via higher layer signaling.

When the correction command is signaled in the UL grant, assuming thatUL HARQ is synchronous, the signaling timing configuration can besimplified such that the command signaling is done in particular ULgrants such as the UL grant associated with a pre-defined HARQ process,for example, HARQ process #1. But, even in this case, it is notnecessary to signal the correction commands in all the associated ULgrant channels. For example, the signaling may occur in every Nassociated grant channel for N>=1, which would be equivalent to onecommand signaling in every N HARQ cycle period. The signaling timing (orassociated parameters) may be reconfigured on a semi static rate.

FIG. 3 shows an example of the disclosed PC method when the PCcorrection command is conveyed in the UL grant associated with HARQprocess #1 and N is set to 2. In this example, the PC update rate is 8msec, assuming the number of HARQ processes is 4 and theinter-transmission time interval (TTI) is equal to 1.

When WTRU 20 receives one correction command from the serving eNodeB 30in an UL grant (or possibly accumulated correction commands in multipleUL grants) since the last Tx PSD adjustment, it shall derive acorrection factor, Δ_(closed), from the received correction command (orafter combining multiple correction commands if more than one command isreceived) for the next PSD adjustment.

WTRU 20 then adjusts the transmit PSD of the data channel according toEquation (1) (or Equation (2)) using the derived correction factor, themost recent open loop PSD, and a power offset associated with thegranted MCS. The resulting Tx PSD shall be applied to the very beginning(first SC-FDMA symbol) of the next UL TTI for the data channel andremain constant until the next PSD adjustment, as shown in FIG. 3.

FIG. 4 shows an example of the timing of the disclosed combined PCmethod, assuming that UL HARQ is a synchronous scheme with 4 HARQprocesses and that WTRU 20 is scheduled to send a data packet (e.g. aHARQ process) every TTI (e.g, inter−TTI=1). In addition, eNodeB 30 sendsa PC correction command only in the UL grant associated with HARQprocess 1. In this case, the WTRU Tx power update period is 4 TTIs(e.g., 4 msec).

As illustrated in FIG. 4, in the initial UL transmission, since theremay be no PC correct command available, WTRU 20 sets its transmit powerbased only on the open loop component (i.e., the weighting factor, α, iszero in Equation (1)). Before the next HARQ transmission time (one HARQcycle time), eNodeB 30 sends a correction command in the grant channelin the HARQ process 1 associated DL control channel, where the commandwas determined based on the link quality (power or SINR) of the firsttwo HARQ processes. If WTRU 20 correctly receives the correctioncommand, WTRU 20 then calculates its transmit PSD_(TX) based on thecombined open loop and closed loop scheme and applies the PSD_(TX) tothe following HARQ processes.

FIG. 5 illustrates another example of the disclosed combined PC timingwhere inter-TTI is two. In this case, the UL PC update period is 8 TTIs(8 msec).

When there is no recent closed loop correction command (for example, dueto recent scheduled UL data transmission, say, UL DTX), WTRU 20 may setits Tx PSD by relying on the open loop. In this case, the weightingfactor, α, in Equation (1) is set to zero as in the case of initial TxPSD setting.

Alternatively, WTRU 20 may set the Tx PSD based on the pathlossvariation between the time before the DTX and the time before resumingthe UL transmission. If the UL DTX is short, the WTRU may use Equation(2) by setting α to zero, such thatPSD _(Tx)(n)=PSD′ _(Tx)(n−1)+(PSD _(open)(n)−PSD_(open)(n−1))+Δ_(MCS)(n)  Equation (7)where n is the Tx PSD setting time before resuming the UL transmissionand (n−1) is the PSD setting time before the DTX. An example of thetiming of this case is shown in FIG. 6.

In another alternative, WTRU 20 may apply a power offset relative to themost recent PSD for physical uplink control channel (PUCCH), ifavailable. Even though there was no UL data transmission, there may beUL control signaling (such as CQI and ACK/NACK) for DL. In this case,since the UL control channel is also power controlled based on Equation(1), (but using different parameters and update rate), the UL controlchannel Tx PSD for the data channel Tx PSD may be used as follows:PSD _(Tx)(data)=PSD _(Tx)(control)+Δ_(control)(data,control)  Equation(8)where PSD_(Tx)(control) is the most recent PSD (or PSD averaged over therecent updates) for the UL control channel and Δ_(control)(data,control) represent the control channel power offset relative to the TxPSD for data.

If the DTX period is long, then WTRU 20 PSD_(Tx) may be determined rightafter the DTX based on open loop only as is the case of the initialPSD_(Tx) setting.

FIG. 7 shows an example of the proposed combined PC scheme, includingDTX.

Typically, the UL grant assignment (e.g. assigned MCS and TBS) in the DLcontrol channel is tied up with the link quality (such as received PSDor SINR) of the UL data transmission. Another method is disclosedwherein an eNodeB 30 processor 125 may assign the UL grant (MCS and TBS)for WTRU 20 such that the grant assignment represents the link quality(e.g. SINR) received at eNodeB 30. In this case, WTRU 20 may derive itsTx PSD as follows:PSD _(Tx) =PSD _(open) +α·f(UL grant assignment,SINR_(T))+Δ_(MCS)(dBm);  Equation (9)where PSD_(open), α, and, Δ_(MCS), respectively, are the same as definedabove. f (UL grant assignment, SINR_(T)) is a correction factor in dBwhich replaces the power correction factor, Δ_(closed), in Equation (1).SINR_(T) is the target SINR in dB. The grant based correction factor, f(UL grant assignment, SINR_(T)), can be expressed by the following:f(UL grant assignment,SINT _(T))=SINR _(T) −E{SINR _(est)(UL grantassignment)};  Equation (10)where SINR_(est) (UL grant assignment) represents the eNodeB receivedSINR estimate which WTRU 20 derives from the UL grant assignment.E{SINR_(est)} denotes the estimated SINR average over time such asE{SINR_(est)(grant^(k))}=ρ·E{SINR_(est)(grant^(k-1))}+(1−ρ)·E{SINR_(est)(grant^(k))}  Equation(11)where grant^(k) represents the k-th received UL grant assignment and ρis the averaging filter coefficient, 0≦ρ≦1. The estimation of SINR_(est)(UL grant assignment) at the WTRU can be based on a grant (MCS, TBS)mapping table, which is configurable by the network through higher layersignaling on a semi-static basis.

Similar to Equation (1), the correction factor in Equation (8) may beused to compensate for open loop errors. The main advantage to usingEquation (8) is that it does not require explicit correction commandsignaling in the UL grant in the DL L1/L2 control channel (resulting inreduced signaling overhead), while Equation (1) (and Equation (2)) needsthe explicit command to be signaled in the UL grant (and/or the DLscheduling). Using Equation (3), the closed loop component may be basedon the UL grant assignment (e.g., MCS and/or TBS), without the explicitcorrection command signaling in the UL grant in the DL L1/L2 controlchannel.

However, Equation (9) may not be applicable for some cases such aspersistent scheduling and grant (e.g. MCS) mismatching (i.e., theassigned MCS does not accurately represent the received SINR).Accordingly, the WTRU Tx PSD setting may be switched between Equation(1) and Equation (8).

Through higher layer correction factor type signaling, wherein eNodeB 30(or the network 10) signals to WTRU 20 which one (Equation (1) orEquation (8)) is to be used for the WTRU Tx power setting. In this case,it is preferable that the correction factor type signal is configurableby network 10 on a semi-static basis and per WTRU basis.

Alternatively, a one-bit MCS mismatching indicator may be introduced inthe DL L1/2 control signaling. For example, bit-1 may indicate to useEquation (1), and bit-0 may be used to indicate Equation (8).

In another alternative, one of the explicit correction command levelsmay be used to indicate the use of Equation (8). This alternativeassumes Equation (1) is the default PC method. As such, eNodeB 30 setsone of the correction command levels in the UL grant to indicate the useof Equation (8). For example, when the correction command in Equation(8) is three-bits long, one of the 8 command level, e.g., ‘000’, is setfor WTRU 20 to use Equation (8).

A flow diagram of the disclosed combined open-loop and closed method ofdetermining the TPC is shown in FIG. 8. Processor 115 of WTRU 20performs open loop power control based on path loss measurement, bydetermining a target power spectral density PSD Target (Step 800) and afiltered pathloss (L) (Step 801). WTRU 20 then determines a closed loopcomponent using a power control correction command received at receiver116 through the UL grant channel (Step 802). Upon receiving thecorrection command, receiver 116 forwards the correction command toprocessor 115 for determining a correction factor Δ_(closed) (Step 803).Processor 115 then calculates a correction factor Δ_(closed). (Step804). Processor 115 then combines the open loop PC with the closed loopcomponent to determine the transmit power control. (Step 805).

In a disclosed method of TPC for non-scheduled data (e.g., VoIP), thereare several options for the WTRU to set its TX PSD: i) relying on theopen loop PSD only, ii) for the closed loop part, the eNodeB transmitsUL grants in particular instants (in time) where the UL grant conveysthe correction command. In this case, the UL grant format (and/or thecorrection command format) may be different than that for scheduleddata; or iii) applying a power offset relative to the most recent PSD(or PSD averaged over the recent updates) for PUCCH, if available.

$\begin{matrix}{{{PSD}_{Tx} = {\underset{\underset{{PSD}_{open}}{︸}}{P_{0} + {SINR}_{Target} + {\alpha \cdot {PL}}} + {\beta \cdot \Delta_{closed}} + {\Delta_{MCS}\mspace{14mu}\left( {{dB}\; m} \right)}}};} & {{Equation}\mspace{14mu}(12)}\end{matrix}$where P₀ is a cell-specific parameter (in dBm) including UL interferencelevel etc, which is signaled by the eNodeB via higher layer signaling.

-   -   SINR_(Target) is a WTRU (or a subset of WTRUs) specific        parameter (in dB), allowing the eNodeB to set classes of service        for the UE (or subset of UEs). SINR_(Target) may be a function        of pathloss to the serving cell and some neighboring cells.        SINR_(Target) can be configured by the serving eNodeB on a        semi-static basis and then signaled to the UE (or subset of UEs)        via higher layer signaling;    -   PL is the downlink pathloss (in dB);    -   λ is a cell specific pathloss compensation factor for fractional        power control where 0<α<=1.α can be configured by the eNodeB on        a semi-static basis and signaled via higher layer signaling;    -   Δ_(closed) is a power correction factor in dB which is        determined based on a closed loop mechanism;    -   ∝ is a weighting factor to enable (∝=1) or disable (∝=0) the        closed loop component, depending on the availability of the DL        control channel carrying the closed loop correction command. The        weighting factor is determined autonomously by the WTRU via        detecting the presence of the PC correction command. It is        assumed that the WTRU is informed via higher layer signaling        from the eNodeB with regard to where and when the command        signaling exists. For instance, in the initial UL transmission,        since there may be no correct command available from the eNodeB,        the WTRU sets ∝=0;    -   Δ_(MCS) is a power offset per granted MCS. Typically, the power        offsets for the individual granted MCS are known by both the        WTRU and the eNodeB.

Since eNodeB 30 knows the Δ_(MCS) in use at a given instance, eNodeB 30may take out the value of Δ_(MCS) from the received PSD when itdetermines a correction command by comparing a resulting received PSD(or SINR) with a target level determined by network 10.

As set forth above, this disclosed method uses an absolute powercorrection factor compared to the open loop based PSD. As such, fromEquation (12), the WTRU Tx PSD at the n^(th) update instance isexpressed as follows:

$\begin{matrix}\begin{matrix}{{{PSD}_{Tx}(n)} = {{{PSD}_{open}(n)} + {\alpha \cdot {\Delta_{closed}(n)}} + {\Delta_{MCS}(n)}}} \\{= {{{PSD}_{Tx}^{\prime}\left( {n - 1} \right)} +}} \\{\left( {{{PSD}_{open}(n)} - {{PSD}_{open}\left( {n - 1} \right)}} \right) + {\alpha \cdot}} \\{{\left( {{\Delta_{closed}(n)} - {\Delta_{closed}\left( {n - 1} \right)}} \right) + {\Delta_{MCS}(n)}};}\end{matrix} & {{Equation}\mspace{14mu}(13)}\end{matrix}$where PSD_(Tx)(n−1) represents the (n−1)^(th) Tx PSD without the poweroffset per granted MCS, which is given byPSD_(Tx)(n−1)=PSD_(Tx)(n−1)−Δ_(MCS)(n−1).

Since the total WTRU transmit power is constrained by the maximumtransmit power level, denoted by P_(max), of the WTRU, the total WTRUtransmit power, denoted by P_(Tx), is expressed as:P _(Tx)=min{P _(max),(10·log₁₀(M)+PSD _(Tx))}(dBm);  Equation (14)where M is the number of assigned RBs.

Accordingly, the actual WTRU transmit PSD may be represented as:PSD _(Tx) ^(actual) =P _(Tx)−10·log₁₀(M)(dBm)  Equation (15)

It should be noted that the UL PC in Equation (15) is implemented byprocessor 115 of WTRU 20.

In accordance with the disclosed PC method for non-scheduled data, WTRU20 calculates the open loop PSD as follows:PSD _(open) =P ₀+SINR_(Target) +λ·PL(dBm)  Equation (16)where

-   -   The target SINR, SINR_(Target), may be adjusted through an outer        loop mechanism at serving eNodeB 30 according to Quality of        Service (QoS) (like target BLER) and be also a function of the        pathloss measurements to the serving cell and neighboring cells;        and    -   PL is the filtered pathloss in dB, including shadowing, from the        serving eNodeB to the WTRU. The WTRU continuously (or        periodically) measures the instantaneous pathloss based on the        DL RS whose transmit power is known at the WTRU. A filtering        method is then applied to the pathloss measurements, such as        PL _(k) =ρ·PL _(k-1)+(1+ρ)·PL _(k)  Equation (17)        where PL_(k) and PL_(k-1) represent the filtered pathloss at the        k-^(th) instance and (k-1)-th instant, respectively. L_(k) is        the instantaneous pathloss at the k-^(th) instant. ρ is a filter        coefficient, 0≦ρ≦1, which is generally determined by WTRU 20,        depending on pathloss variation, fast fading rate, the time of        UL transmission, etc. Alternatively, a moving averaging method        may be considered for the pathloss filtering.

The closed loop component is determined by processor 115 similar to thatwhich is disclosed above.Δ_(closed)=┌ESINR_(est)−SINR_(target)┘  Equation (18)where ESINR_(est) and SINR_(target) denotes the effective SINR (ESINR)estimate at the receiver and target SINR, respectively, of the powercontrolled channel(s) in dB. [x] denotes a correction value in thecorrection set, which is nearest to x.

Similar to the methods disclosed above, when the correction command issignaled in the UL grant, assuming that UL HARQ is synchronous, thesignaling timing configuration can be simplified such that the commandsignaling is done in particular UL grants such as the UL grantassociated with a pre-defined HARQ process.

For non-scheduled data (e.g., VOIP), when there is no recent closed loopcorrection command (for example, due to recent scheduled UL datatransmission, say, UL DTX), WTRU 20 may set its Tx PSD by relying on theopen loop: in this case, the weighting factor, ∝, in Equation (13) isset to zero as in the case of initial Tx PSD setting. WTRU 20 mayalternatively set its TX PSD based on the pathloss variation between thetime before the DTX and the time before resuming the UL transmission: ifthe UL DTX is short, the WTRU may use Equation (2) by setting β to zero,such thatPSD _(Tx)(n)=PSD _(Tx)(n−1)+(PSD _(open)(n)−PSD_(open)(n−1))+Δ_(MCS)(n);  Equation (19)where n is the Tx PSD setting time before resuming the UL transmissionand (n−1) is the PSD setting time before the DTX. An example of thiscase is shown in FIG. 4.

Alternatively, WTRU 20 may apply a power offset relative to the mostrecent PSD for PUCCH, if available. Even though there was no UL datatransmission, there may be UL control signaling (such as CQI andACK/NACK) for DL. In this case, since the UL control channel (PUCCH) isalso power controlled based on Equation (12), (but using differentparameters and update rate), the UL control channel (PUCCH) Tx PSD maybe used for the data channel (PUSCH) Tx PSD as follows:PSD _(Tx)(PUSCH)=PSD _(Tx)(PUCCH)+Δ_(control)(PUSCH,PUCCH);  Equation(20)where PSD_(Tx)(PUCCH) is the most recent PSD (or PSD averaged over therecent updates) for the UL control channel (PUCCH) andΔ_(control)(PUSCH, PUSCH) represent the control channel (PUCCH) poweroffset relative to the Tx PSD for PUSCH.

For a sounding pilot, its Tx PSD, PSD_(Tx)(pilot), may be biased by apilot power offset relative to the data TX PSD, PSD_(Tx)(data), suchthatPSD _(Tx)(pilot)=PSD _(Tx)(data)+Δ_(pilot)(data,pilot)  Equation (21)

where Δ_(pilot)(data, pilot) represent the pilot power offset which maybe a WTRU-specific parameter configured by the eNodeB on a semi-staticbasis.

For control signaling in UL, it is preferred to use different parameters(such as target PSD) and a faster update rate than for data. Inaddition, we prefer that the reference channel measured for correctioncommands for control signaling is the control channel itself and thecorrection command for control is conveyed in the DL scheduling. Thenumber of bits for the correction command for control may be differentthan for data, where the number of command bits may be a semi-staticconfigurable parameter per WTRU basis. However, we may maintain arelative average power offset between the data and control channels suchasE(PSD _(Tx)(data))=E(PSD_(Tx)(control))+Δ_(control)(data,control)  Equation (22)whereE(PSD_(Tx)(data)) represents the average PSD for data channel in dBm;E(PSD_(Tx)(control)) represents the average PSD for control channel indBm; and

*Δ_(control)(data, control) is a power offset between the data channeland the control channel.

In another disclosed method of UL PC, a combined Open Loop/Closed LoopUL PC with Interference Mitigation for Shared Data Channel is used. Inaccordance with this method, WTRU 20 controls its transmitted PSD for ULchannels. If the bandwidth allocation (e.g., RB allocation) of WTRU 20varies, then the WTRU total transmit power varies such that the PSD iskept constant.

As described in the disclosed methods above, WTRU 20 performs open loopPC based on pathloss measurement and system parameters. WTRU 20 thencorrects its PSD using some form of closed loop PC to compensate for theopen loop errors. It should be noted that for each UL scheduled WTRU,CQI information is periodically signaled from eNodeB 30 for AMC andscheduling. Hence, the closed loop PC component of this disclosed methoddoes not need any additional PC command signaled by eNodeB. In order tomitigate inter-cell interference in the neighboring cell(s), WTRU 20incorporates an interference load indicator from the strongestneighboring cell.

In accordance with this method, for the UL shared data channel, in theinitial transmission phase, WTRU 20 derives its transmitted PSD,PSD_(Tx), based on DL reference signal (RS) as follows:PSD _(Tx)=SINR_(T) +PL+IN ₀ +K+Δ(IoT _(S))−10·log 10(BW _(RU) ·N_(RU));  Equation (23)where SINR_(T) is the target SINR in dB at serving eNodeB 30. PL is thepathloss in dB, including shadowing, from serving eNodeB 30 to WTRU 20,where WTRU 20 measures the pathloss based on the DL RS whose transmitpower is known at WTRU 20 via DL Layer 2/Layer 3 signaling, IN₀ is theUL interference and noise power in dBm, measured at serving eNodeB 30. Kis a power control margin set by serving eNodeB 30.

It is preferable that the target SINR for WTRU 20 (or a sub-group ofWTRUs) is adjustable using an outer loop PC scheme according to a linkquality metric (such as BLER) at serving eNodeB 30. In addition, in thecase of UL Multiple In Multiple Out (MIMO), the target SINR depends alsoon the selected MIMO mode, which takes into account the fact thatdifferent MIMO modes require different SINR for a given link quality.Δ(IoT_(S)) represents the UL load control step size, which is a functionof the UL interference load (e.g. interference over thermal) indicatorof the strongest neighboring cell, IoT_(S), where the strongestneighboring cell is determined at WTRU 20, based on pathlossmeasurements from the individual neighboring cell to WTRU 20. It isassumed that each cell 40 broadcasts an UL interference load bitperiodically (similar to the relative grant in HSUPA), so that WTRU 20can decode the indicator bit from the selected strongest neighboringcell.

For example, Δ(IoT_(S)) may have values as follows:

${\Delta\left( {IoT}_{S} \right)} = \left\{ \begin{matrix}{{\delta < 0},} & {{{when}\mspace{14mu}{IoT}_{S}} = {1\mspace{14mu}{{or}\mspace{14mu}}^{``}{down}\mspace{14mu}{command}^{''}}} \\{0,} & {{{{when}\mspace{14mu}{IoT}_{S}} = 0},{\,^{``}{DTX}},^{''}\mspace{14mu}{{or}{\mspace{11mu}\;}{\,^{``}{up}}\mspace{14mu}{command}^{''}}}\end{matrix} \right.$where δ is a predefined system parameter, for example, δ=−1 or −2 dB.With the use of Δ(IoT_(s)), inter-cell interference in neighboring cellscan be mitigated.

Since WTRUs at cell center inject less interference into other cellsthan those at cell edge, a fraction of the load control step size isconsidered as follows:

$\delta = \left\{ \begin{matrix}{\delta,} & {{for}\mspace{14mu}{WTRUs}{\mspace{11mu}\;}{at}\mspace{14mu}{cell}\mspace{14mu}{edge}} \\{\frac{\delta}{x},} & {{{for}\mspace{14mu}{cell}\mspace{14mu}{interior}\mspace{14mu}{WTRUs}\mspace{14mu}{where}\mspace{14mu} x} > 1}\end{matrix} \right.$

WTRU 20 may make a decision on whether it is at cell edge or at cellinterior based on a pathloss ratio between its serving cell and thestrongest neighboring cell, for example.

If (pathloss_serving_cell-pathloss_strongest_neighboring_cell)<R (dB),x=4; where R represents the virtual boundary layer between the cellinterior zone and cell edge zone. The parameter R may be broadcast byeNodeB 30 semi-statically.

After the initial transmission phase, WTRU 20 PSD_(TX) is calculated asfollows:PSD _(TX)=SINR_(T) +PL+IN ₀ +K+Δ(IoT _(S))+α·f(CQI,SINR_(T))−10·log10(BW _(RU) ·N _(RU))  Equation (24)where f (CQI, SINR_(T)) is a correction factor based on the UL CQI, andthe corresponding target SINR where both the CQI and the target SINR aresignaled from serving eNodeB 30; α, where 0≦α≦1, is a weighting factorwhich may be determined according to channel conditions and CQIavailability (or UL transmission pause). For instance, in the case wherethere is no UL CQI (UL MCS or grant information) available from eNodeB30 due to no scheduled UL data transmission, the weighting factor, α, isset to zero, meaning that WTRU 20 relies on open loop PC only (such asPC for the random access channel (RACH)); otherwise, it is set to beless than or equal to one (1).

The correction factor, f (CQI, SINR_(T)), in Equation 24, is used tocompensate for open loop PC related errors, including the pathlossmeasurement error due to non-perfect reciprocity in UL and DL in FDD andWTRU 20 transmitter impairment due to non-linear WTRU transmitter poweramplification. In addition, the correction factor is used to compensatefor target quality mismatch due to different channel conditions. Hence,the quality of the power controlled channel(s) is maintained along witha given target quality (like target SINR).

Taking into account the fact that the UL CQI (UL MCS or grantinformation) represents the SINR received at eNodeB 30, the correctionfactor can be calculated such as,f(CQI,SINT_(T))=SINR_(T)−E{SINR_(est)(CQI)}(dB);  Equation (25)where SINR_(est)(CQI) represents the eNodeB received SINR estimate,which the WTRU derives from the UL CQI feedback. E{SINR_(est)(CQI)}denotes the estimated SINR average over time such as by the following:E{SINR_(est)(CQI ^(k))}=ρ·E{SINR_(est)(CQI^(k-1))}+(1−ρ)·E{SINR_(est)(CQI ^(k))};  Equation (26)where CQI^(k) represents the k-th received CQI and ρ is the averagingfilter coefficient, 0≦ρ≦1.

The correction factor, given above, in Equation (25), by the differencebetween the target SINR and the estimated SINR (derived from thereported CQIs), represents the open loop PC related errors which need tobe compensated.

The WTRU total transmit power should be within the maximum power level,P_(max), and the minimum power level, P_(min), in dBm, respectively,where the maximum and minimum power levels are determined based on WTRUclass.

eNodeB 30 preferably signals parameters, including a target SINR level,SINR_(T), which is a WTRU (or a sub-group of WTRUs)-specific parameter,where the target SIR may be adjusted through an outer loop mechanismbased on QoS like target BLER. The target SINR may be also a function ofthe pathloss measurement. The signaling of the target SIR is done viain-band L1/2 control signaling upon its adjustment. A power controlmargin, K, which is an eNodeB-specific parameter is also signaled byeNodeB 30. K is preferably semi-static and signaled via the broadcastchannel (BCH). It should be noted that even though K is assumed to beseparately signaled along with the other parameters, it may be embeddedin the target SINR, i.e., SINR_(T) (after embedding) SINR_(T)+K (dB). Inthis case, explicit signaling of K to WTRU 20 is not required.

eNodeB 30 further signals a total UL interference and noise level, IN₀,which is averaged across all the sub-carriers (or RBs) in use, or asubset of the sub-carriers. This parameter is preferably derived byserving eNodeB 30 (and possibly signaled via BCH). The update rate forthis signaling is generally relatively slow. The maximum and minimum ULpower level, P_(max) and P_(min) is also signaled by eNodeB 30. Whicheach may be WTRU capability dependent parameters, or may be expresslysignaled by eNodeB 30.

A UL channel quality indicator, CQI (e.g. UL MCS or grant information),which is signaled originally for the purpose of UL AMC (with a maximumsignaling rate of once per TTI, e.g. 1000 Hz).

A CQI mapping rule (or bias between CQI and measured SINR), which theeNodeB uses for CQI feedback generation. This rule or parameter may becombined into the target SINR. In this case, explicit signaling of therule (or parameter) is not required.

An UL interference load indicator from each eNodeB.

The semi-static parameter R which represents the virtual boundary layerbetween the cell interior zone and cell edge zone.

The disclosed PC method do not require additional feedback PC commandsother than the above listed system parameters including the target SINR,cell interference/noise level, and reference signal transmit power andconstant value, which can be broadcast (or directly signaled) to WTRUson a slow rate basis.

It is designed to be flexible and adaptive to dynamic system/linkparameters (target SINR and inter-cell interference loading condition)and channel conditions (path loss and shadowing), in order to achievethe E-UTRA requirements.

Further, this disclosed method is compatible with other link adaptationschemes such as AMC, HARQ, and adaptive MIMO.

In an alternative method of inter-cell interference mitigation, insteadof broadcasting an interference load indicator from each eNodeB, servingeNodeB 30 may co-ordinate inter-cell interference levels with othercells 40 and incorporate them through adjusting the target SIR, powercontrol margin K or possibly P_(max) accordingly.

Although features and elements are described above in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) or Ultra Wide Band (UWB)module.

What is claimed is:
 1. A method for controlling transmit power of awireless transmit receive unit (WTRU) comprising: determining an openloop uplink (UL) power control (PC) component based on pathlossmeasurement, wherein the open loop PC component comprises acell-specific parameter and a WTRU-specific parameter, and wherein thecell-specific and WTRU-specific parameters are provided from higherlayers; determining a closed loop PC component including a correctionfactor, wherein the correction factor is based on a PC correctioncommand signaled in a UL grant associated with a hybrid automatic repeatrequest (HARQ) process; combining the open loop PC component and theclosed loop PC component with a delta factor related to an offset valueto determine a transmit power, wherein the offset value is related to amodulation and coding scheme (MCS); and applying the transmit power inaccordance with a timing of the HARQ process.
 2. The method of claim 1,further comprising receiving the PC correction command.
 3. The method ofclaim 2, wherein the PC correction command is received at apre-configured signaling time.
 4. The method of claim 1, wherein theopen loop PC component is based on a pathloss variation.
 5. The methodof claim 4, wherein the pathloss variation is determined based on avariation between the pathloss prior to a discontinuous transmission anda time before resuming an UL transmission.
 6. The method of claim 1,wherein the PC correction command includes multiple command bitsdetermined based on link quality.
 7. A method for controlling transmitpower of a wireless transmit receive unit (WTRU) comprising: determiningan open loop uplink (UL) power control (PC) component based on pathlossmeasurement; determining a closed loop PC component including acorrection factor, wherein the correction factor is based on a PCcorrection command including multiple command bits determined based onlink quality; combining the open loop PC component and the closed loopPC component with a delta factor related to an offset value to determinea transmit power, wherein the offset value is related to a modulationand coding scheme (MCS), and wherein the correction factor is determinedusing the following equation:Δ_(closed)=┌ESINR_(est)−SINR_(target)┘; where ESINR_(est) andSINR_(target) denotes the effective signal to interference noise ratio(ESINR) and target a SINR.
 8. The method of claim 1, wherein thetransmit power is applied from the beginning of an uplink transmit timeinterval (TTI) until a transmit power update is received.
 9. The methodof claim 8, wherein a value of the correction factor is zero (0) in aninitial uplink transmission.
 10. A method for controlling transmit powerof a wireless transmit receive unit (WTRU) comprising: determining anopen loop uplink (UL) power control (PC) component based on pathlossmeasurement; determining a closed loop PC component including acorrection factor, wherein the correction factor is an uplink grantassignment; combining the open loop PC component and the closed loop PCcomponent with a delta factor related to an offset value to determine atransmit power, wherein the offset value is related to a modulation andcoding scheme (MCS), and, wherein the grant based correction factor isdetermined using the following equation:f(UL grant assignment,SINT _(T))=SINR _(T) −E{SINR _(est)(UL grantassignment)}; where SINR_(est)(UL grant assignment) represents an eNodeBreceived SINR estimate which WTRU derives from the UL grant assignment.11. The method of claim 10, further comprising receiving a correctionfactor sign and determining whether to use the grant based correctionfactor based on the received correction factor sign.
 12. The method ofclaim 10, further comprising receiving an MCS mismatching indicator anddetermining whether to use the grant based correction factor based onthe received MCS mismatching indicator.
 13. The method of claim 10,further comprising receiving an MCS mismatching indicator anddetermining whether to use an explicit correction command based on thereceived MCS mismatching indicator.
 14. The method of claim 1, furthercomprising determining an interference load indicator based on signalingreceived from a strongest neighboring cell.
 15. The method of claim 14,wherein the transmit power is based on a downlink reference signalwherein the interference load indicator is used to mitigate inter-cellinterference.
 16. A wireless transmit receive unit (WTRU) comprising aprocessor, wherein the processor is configured to: determine an openloop uplink (UL) power control (PC) component based on pathlossmeasurement, wherein the open loop PC component comprises acell-specific parameter and a WTRU-specific parameter, and wherein thecell-specific and WTRU-specific parameters are provided from higherlayers; determine a closed loop power control component including acorrection factor, wherein the correction factor is based on a PCcorrection command signaled in a UL grant associated with a hybridautomatic repeat request (HARQ) process; and combine the open loop PCcomponent, the closed loop PC component and a delta factor related to anoffset value to determine a WTRU transmit power, wherein the offsetvalue is related to a modulation and coding scheme (MCS); and apply thetransmit power in accordance with a timing of the HARQ process.
 17. TheWTRU of claim 16, further comprising a receiver, wherein the receiver isconfigured to receive the PC correction command.
 18. The WTRU of claim17, wherein the PC correction command is received in a pre-configuredsignaling time.
 19. The WTRU of claim 16, wherein the open loop PCcomponent is based on a pathloss variation.
 20. The WTRU of claim 19,wherein the pathloss variation is determined based on a variationbetween the pathloss prior to a discontinuous transmission (DTX) and atime before resuming an UL transmission.
 21. The WTRU of claim 16,wherein the PC correction command includes multiple command bitsdetermined based on link quality.
 22. A wireless transmit receive unit(WTRU) comprising a processor, wherein the processor is configured to:determine an open loop uplink (UL) power control (PC) component based onpathloss measurement; determine a closed loop power control componentincluding a correction factor, wherein the correction factor is based ona PC correction command including multiple command bits determined basedon link quality; and combine the open loop PC component, the closed loopPC component and a delta factor related to an offset value to determinea WTRU transmit power, wherein the offset value is related to amodulation and coding scheme (MCS), and wherein the correction factor isdetermined using the following equation:Δ_(closed)=┌ESINR_(est)−SINR_(target)┘; where ESINR_(est) andSINR_(target) denote the effective signal to interference noise ratio(ESINR) and target a SINR.
 23. The WTRU of claim 16, further comprisinga transmitter, wherein the transmitter is configured to apply thetransmit power to the beginning of a next uplink transmit time interval(TTI) until a next transmit power update.
 24. The WTRU of claim 23,wherein a value of the correction factor is zero (0) in an initialuplink transmission.
 25. A wireless transmit receive unit (WTRU)comprising a processor, wherein the processor is configured to:determine an open loop uplink (UL) power control (PC) component based onpathloss measurement; determine a closed loop power control componentincluding a correction factor, wherein the correction factor is anuplink grant assignment; and combine the open loop PC component, theclosed loop PC component and a delta factor related to an offset valueto determine a WTRU transmit power, wherein the offset value is relatedto a modulation and coding scheme (MCS), and wherein the grant basedcorrection factor is determined using the following equation:f(UL grant assignment,SINT _(T))=SINR _(T) −E{SINR _(est)(UL grantassignment)}; where SINR_(est)(UL grant assignment) represents an eNodeBreceived SINR estimate which WTRU derives from the UL grant assignment.26. The WTRU of claim 25, wherein the processor is configured todetermine whether to use the grant based correction factor based on areceived correction factor sign.
 27. The WTRU of claim 25, wherein theprocessor is configured to determine whether to use the grant basedcorrection factor based on a received MCS mismatching indicator.
 28. TheWTRU of claim 25, wherein the processor is configured to determinewhether to use an explicit correction command based on a received MCSmismatching indicator.
 29. The WTRU of claim 16, wherein the processoris configured to determine an interference load indicator based onsignaling received from a strongest neighboring cell.
 30. The WTRU ofclaim 29, wherein the interference load indicator is used to mitigateinter-cell interference.